1. Field Of The Invention
This invention relates to apparatus for cleaning the interior surfaces of tubes, and more particularly, to a fluid controlled jetting apparatus which jets fluid at high pressure on both an outward stroke and a return stroke of a lance assembly therein and relieves the high pressure at the end of the return stroke.
2. Description Of The Prior Art
Previously known fluid powered jetting apparatus generally fall into one of two categories. In the first category, fluid is pumped to the lance directly. Jetting apparatus of this type are disclosed in U.S. Pat. Nos. 1,982,590 to Church et al., and 3,246,847 to Hammelmann. These devices have the advantage of delivering full pump pressure to the spray head or nozzle on the end of the lance, but they are relatively complex and require close tolerance valving and moving parts with the various wetted areas separated by high maintenance elastomeric seals.
In the other type of previously known fluid powered jetting apparatus, the fluid is fed to the lance indirectly from the piston side of the device. That is, the device acts similar to a hydraulic cylinder. Such an apparatus is shown in U.S. Pat. Nos. 4,137,928 and 4,225,362 to Sentell. These devices have the advantage of requiring only simplified control valving and no close tolerances other than the lance wiper gland separating the rod into the cylinder from the environment. However, they have a disadvantage in that a large percentage of the pressure is consumed as viscous friction losses across the piston before the fluid reaches the lance.
The tube jetting apparatus of the present invention takes advantage of the simplicity of the indirect feed devices, but fluid is fed to the lance from the high pressure lance side of the device rather than the low pressure piston end of the device. Tube jetting apparatus built according to the present invention will have a greater efficiency than prior art devices of the second type already discussed. The present invention also has the advantage of jetting fluid on the return stroke, as well as the outward stroke. An automatic end of cycle pressure release system lowers the pressure on the entire lance nozzle and lance reciprocating system at the end of the return stroke which is generally the only time that an operator must be in close proximity to the apparatus.
In cleaning articles such as heat exchangers with U-bend tubes, the jetting lance must be stopped at a predetermined point to avoid a collision between the lance and the U-bend region of the tube being cleaned. In such a case, it is desired to limit the outward stroke of the jetting lance to a predetermined distance. Generally, a sleeve or plug is attached to the lance itself by a fastening means such as set screws, such as in U.S. Pat. No. 4,344,570 to Paseman, and this sleeve or plug will stop outward motion of the lance when it contacts a shoulder in the apparatus. A problem with such stroke limiting devices is that the set screws must be set very tightly against the surface of the lance to hold the sleeve or plug when it engages the shoulder. Frequently, setting the set screws will damage the surface of the lance, or the sleeve or plug will move slightly which causes the set screw to drag along the surface, again causing damage to the lance. This is a problem if the lance is then later used for longer strokes and this damaged area passes through sealing members.
The jetting apparatus of the present invention solves this problem by providing a mechanical stroke limiter which utilizes a collet means which tightens around and grippingly engages the lance when a collet engaging means contacts a shoulder in the apparatus. A collet support means may be used and is attached to the lance by set screws, but the collet support means absorbs very little axial force. Therefore, it is generally not necessary to tightly engage the set screws with the lance, nor is it likely that the collet support means will move axially along the lance and thereby damage it.